1. Field of the Invention
This invention relates to transport aircraft galley systems, and more particularly, to a liquid sensing system that monitors leak and fault conditions of circulation of a two phase working fluid used by an aircraft cooler.
2. Description of Related Art
Aircraft galley systems for modern transport aircraft incorporate food carts which are cooled to prevent food spoilage prior to use by the cabin attendants for distribution of food to the passengers. These food carts have in the past been interfaced with cold air supply systems in the galley designed to cool the interiors of the food carts. Such cool air distribution systems were generally co-located with the balance of the galley and interface to the food carts by means of gaskets connecting the food carts to a plenum containing the cool air.
As space in modern aircraft has become more at a premium and more efficient means of cooling the carts has become necessary, a need for alternatives to such systems emerged. Furthermore, FDA rulings lowered the required temperature at which the interior of the food carts must be kept to prevent food spoilage. Additionally, it has become more desirable to remove refrigeration equipment from the galley compartment and to find other means to properly cool the food carts without locating the entire refrigeration system in the galley area. In order to be compatible with modern transport aircraft requirements, it has become important to have an increased degree of safety and modularity for any aircraft system incorporating electronics or electric pumps. In any event, it is important that any system that interfaces with either food or the cabin area can be configured to provide a wide range of cooling capacity as a function of the food and food carts that are to be interfaced with such a system.
Such cooling systems require control systems to maintain temperatures within the food carts within precise limits to prevent food spoilage or freezing. The present invention satisfies these and numerous other requirements for transport aircraft.
The present invention overcomes the shortcomings of previously known systems for cooling food carts in aircraft. The system of the invention serves not only to remove the bulk of the refrigeration system from the galley area but also obviates the need to accommodate bulky air ducts that would supply cooled air from refrigeration stations directly to the carts. Additionally, the system allows low temperatures to be readily achieved in a very controllable manner.
In general terms, the invention employs an intermediate working fluid to transfer heat from a cart or carts to a remote chiller or chillers. The components of the system may be advantageously positioned in the aircraft and do not have to be contained in a single location. More specifically, the invention utilizes a plurality of heat exchangers to effect a cooling of the carts wherein heat from the food cart is first transferred to an airflow; heat from the airflow is then transferred to an intermediate working fluid which is circulated between a location immediately adjacent the food carts and a remote chiller; heat from the intermediate working fluid is subsequently transferred to the chiller working fluid; and finally, heat from the chiller working fluid is expelled to ambient air.
While the chiller working fluid may undergo a phase change in order to transfer heat from the intermediate working fluid to the ambient air, the intermediate working fluid typically remains in its liquid phase throughout its circulation. A recirculation pump serves to circulate the intermediate working fluid through a distribution system that may link a plurality of chillers to a plurality of food carts. An expansion tank accommodates the expansion and contraction that the intermediate working fluid undergoes during its circulation. Each of the chillers cycles the associated chiller working fluid between a condenser and evaporator in a conventional manner whereby an expansion valve is relied upon to control the phase change therebetween.
The temperature of the food cart is regulated by a combination of controls. The speed of a fan circulating air flowing over the heat exchanger for the intermediate working fluid and directing the air cooled in this manner through the food cart may be varied so as to influence the rate of heat transfer between the food cart and the intermediate working fluid. A variable flow valve may be used to control the flow of intermediate working fluid to each cart, while the flow velocity of the intermediate working fluid circulating in the entire distribution system may be controlled by varying the speed of the recirculation pump. Finally, each of the chillers may be turned on or off depending upon the temperature of the intermediate working fluid returning from the food carts. Temperature sensors and pressure sensors are positioned throughout the system to monitor these parameters at appropriate locations in order to allow the operation of the overall system to be properly controlled by the use of electronic controls such as programmable industrial controllers (PIDs).
In another aspect of the invention, the invention provides for a liquid sensing system for a cooler for an aircraft using a two phase working fluid, in which the cooler circulates the two phase working fluid between a cooling heat exchanger and a chiller unit for cooling the two phase working fluid. The liquid sensing system includes a middle liquid level sensor for detecting a middle liquid level of the working fluid and generating a middle liquid level signal, a liquid temperature sensor for sensing temperature of the working fluid and generating a liquid temperature signal, means for generating a flight phase signal indicative of a flight phase of the aircraft; and a recirculation unit for receiving the middle liquid level signal, the liquid temperature signal, and the flight phase signal, the recirculation unit annunciating a working fluid system leak condition based on the middle liquid level signal, the liquid temperature signal, and the flight phase signal. In one aspect of the liquid sensing system, the recirculation unit only evaluates the working fluid system leak condition during a ground flight phase and a cruise flight phase. In another aspect, the recirculation unit requires a confirmation time of the middle liquid level sensor to indicate the absence of working fluid continuously for 15 minutes to annunciate a working fluid system leak condition. In a further presently preferred aspect, the recirculation unit additionally annunciates a system leak based upon a temperature indicated by the liquid temperature sensor following the 15 minute confirmation time of the middle liquid level sensor.
The invention according also provides for a method for sensing leaks in a cooler for an aircraft using a two phase working fluid, the aircraft cooler circulating the two phase working fluid between a cooling heat exchanger and a chiller unit for cooling the two phase working fluid. The method includes the steps of detecting a middle liquid level of the working fluid and generating a middle liquid level signal, sensing temperature of the working fluid and generating a liquid temperature signal, generating a flight phase signal indicative of a flight phase of the aircraft, and receiving the middle liquid level signal, the liquid temperature signal, and the flight phase signal, evaluating a working fluid system leak condition, and annunciating the working fluid system leak condition based on the middle liquid level signal, the liquid temperature signal, and the flight phase signal. In a preferred aspect of the method, the working fluid system leak condition is only evaluated during a ground flight phase and a cruise flight phase. In another aspect, the annunciation of the working fluid system leak condition requires a confirmation time of the middle liquid level signal to indicate the absence of the working fluid continuously for 15 minutes. In another presently preferred aspect, the annunciation of the working fluid system leak condition is based upon the liquid temperature signal following the 15 minute confirmation time of the middle liquid level signal. If the temperature indicated by the liquid temperature signal is greater than or equal to 13 degrees F., and less than or equal to 55 degrees F., then a minor system leak condition is annunciated. If the temperature indicated by the liquid temperature signal is greater than 55 degrees F., then a major system leak condition is annunciated. However, if the flight phase changes during the evaluation of a leak condition, the leak conditions are cancelled.
In another presently preferred aspect, the method further includes sensing a bottom liquid level and generating a bottom liquid level signal, sensing pressure in a working fluid accumulator and generating an accumulator pressure signal, and sensing a discharge pressure of the working fluid and generating a discharge pressure signal, and annunciating a no working fluid failure condition based on the bottom liquid level signal, the accumulator pressure signal, and the discharge pressure signal. A differential pressure is determined based upon the discharge pressure signal and the accumulator pressure signal, and a pump airlock condition is determined when the differential pressure drops below a predetermined pressure for a predetermined period of time. A pump airlock failure condition is determined for a predetermined number of pump airlock conditions.
Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention.